1965 Master Cylinder Question

[48Super]

I just finished up a complete brake system rebuild on my 65 GS and everything works but the pedal is very low and does not feel right. I've bled the system twice with no improvement. I suspect that I may have an issue with the check valve in the master cylinder.

My car has a Bendix-type master cylinder with the screw on lid. In order to maintain the original appearance, I had a stainless sleeve installed in the original cylinder. Now, here is the problem, there are two master cylinder rebuild kits listed for this application. NAPA #UP420 (Raybestos MK420) is supposedly for rebuilding the OEM cylinder only. NAPA #UP234 (Raybestos MK234) is for rebuilding aftermarket cylinders only. The attached pictures show the contents of these kits.

I bought both kits to sure I had the right parts. The piston is identical in both kits and the main difference is that they use two completely different style check valves. Also, the OEM kit does NOT include the return spring.

When I compared the replacement parts to my originals, I found that the check valve parts and return spring did not match the parts in either kit. I decided to use the Aftermarket kit since the return spring I had did not fit the OEM check valve. I think this may be my problem. From the illustrations in the Shop Manual, it appears that the check valve in the OEM (Bendix) kit is meant to fit into a small counterbore at the outlet end of the cylinder. The other style check valve (Morraine) seals against a rubber washer that rests on a flat surface with no counterbore. I think the parts I installed may not be compatible with the my cylinder.

I've ordered a complete new Bendix #11258 replacement master cylinder which has the bail wire type cover but I would really prefer to keep the original part.

What I think I need is to have the correct original return spring for the OEM Bendix type cylinder so I can use the matching style check valve. Possibly, a NORS rebuild kit from another manufacturer may actually have ALL the right parts.

I'd appreciate hearing from anyone who has experience with this problem or suggestions on how to proceed.

[RivNut]

Read through this previous thread and see if anything in it is applicable to you. Pay close attention to what everyone is saying about differences in the Delco-Morraine system and the Bendix system. The thread might not seem applciable to your situation, but there are parts that relate to your problem. Pay particular heed to Jim Cannon's final word on this.

Ed

http://forums.aaca.org/f177/first-gen-dual-master-cylinder-224530.html

Edited April 21, 2013 by RivNut (see edit history)

[48Super]

Ed,

Thanks for your input, that was interesting reading. I did check the bore depth on the original piston and the pistons in the two different rebuild kits. They were all basically the same. I understand that the piston bore depth will affect the position of the piston with respect to the compensating port in the cylinder body and will cause major problems if things aren't right. I think my issue is caused by something else.

[Jim Cannon]

Mike-

Did you "bench bleed" the master cylinder before installing it?

Will the pedal pump up to normal height with a few rapid strokes?

Going back to the link Ed posted, you are sure you have the correct indentation depth in the piston, matching your original. The indentation faces the booster. If the hole facing the booster is too deep, your pedal will be too low when the pin coming out of the booster contacts the bottom of the hole in the piston. This is more important than when the compensating port is covered.

Can you add a picture of the pieces you took out of the original master cylinder, so we can compare them to the parts kit?

I don't have my shop manual with me right now. I thought the check valve rested against the piston seal, which rests against face of the piston (rubber ring between them), with the spring against it, holding them all up against the piston. Are there several little holes in the face of the piston that face into the bore of the master cylinder? I am doing this from memory.

Sequence of assembly: drop in spring, place check valve against end of spring, piston seal, flat rubber ring, slide piston in, lock in with snap ring. Something like that.

I won't have my shop manuals for several weeks. If someone can scan and post the sketch of the internals, that would help me.

[48Super]

Jim,

I did verify the piston I installed had the same depth hole as the original one. I am reinstalling the original master cylinder (which was sleeved) in the original booster. I did not change the actuating rod length. I did not pre-bleed the master cylinder and the pedal does not seem to come up when pumped repeatedly.

I've included a picture of the parts I removed from the original cylinder and the parts that came with the "OEM kit" which I did not use because the kit did not include a new return spring and the original spring was not compatible with the replacement parts. The correct spring would be a constant diameter for the full length, the springs I have are tapered from end to end.

The exploded view of the Bendix master cylinder shows that the original check valve looks like the one in the OEM kit. If I could get the original spring I could use this style check valve. I believe my mistake was in thinking I could substitute the spring and check valve parts from the Morraine type master cylinder into my Bendix cylinder.

If I can't find the right parts or figure out what is wrong, I'll probably just install a complete new Bendix master cylinder which I have on order. I can always install the original one later if I come across the right spring.

Bendix Master Cylinder Parts.pdf

[JZRIV]

Yes you definitely want to keep the original screw lid Bendix MC. They are getting scarce. Have you confirmed 100% the components have been installed properly? do you have a shop manual? The check valve goes in first and seats at the end of the bore with the metal disc towards the spring. Then the spring, then cup seal with cup towards spring (so spring fits inside cup) and then the piston with permanently attached cup seal end in last. Attached is a Raybestos kit I used. I reused my original spring. Make sure the new sleeve was drilled properly to match all the openings. Who sleeved the MC? Did the cup seals seem to fit snug when the piston was installed.

Other than improper bleeding, something is either installed wrong or the sleeve is not right.

It would be unlikley the check valve or the spring would cause a low pedal. If you are not building pressure the primary cup seal (in front of piston) is not sealing for some reason or you have air. Bench bleed the MC before installation.

I added a pic of the counter bore at the end which the check valve must seat in. Again though, I do not think the check valve would prevent you from building a solid pedal. It only keep slight residual or static pressure in the lines when system is at rest.

Edited April 21, 2013 by JZRIV (see edit history)

[Jim Cannon]

I agree with Jason: the residual pressure valve will not prevent you from building pressure. It is there to keep some pressure in the line, to keep all of the cups in the wheel cylinders expanded a tiny bit for a better seal. You could leave it out and never notice the difference.

I have never been able to get all of the air out of a MC without bench bleeding it. Remove the MC from the car and put on a bleeder line that squirts right back into the reservoir. Put the end of the line under the surface of the fluid. Pump very slowly but all the way down. Repeat until no air comes out with the fluid. That is why doing it on the bench is better; you can press the piston in slowly and bottom it. If you see a lot of air bubbles in the brake fluid reservoir, stop and let them settle out (rise to the top), then resume.

Thanks for the scan of the figure. That refreshes my memory. Unfortunately, like many of the drawings in the shop manual, that is a generic picture and not specific to the '65 Riviera.

[48Super]

Jason,

Those pictures helped. I have the same kit shown in your picture but I was unable to use it because I did not have the original spring. Do you have an extra one you can spare? I had to use the spring and check valve parts from the other style kit. Everything is installed properly and I get a solid pedal but it is too low, there does not seem to be any reserve.

My cylinder was sleeved with stainless by Brake & Equipment Warehouse in Minneapolis, they have done nice work for me in the past. I did check the cylinder to make sure all ports looked correct prior to assembly. I bled the entire system twice and can not find any evidence of external leaks. I did drive the car and the brakes will stop it OK but I know the pedal should be higher.

The brakes functioned normally prior to my rebuilding the system. I did the work because I noticed a leaking wheel cylinder and decided to a complete overhaul. The previous owner had not used the car much in last 15-20 years and all the wheel cylinders were the DELCO originals.

According to the troubleshooting guide in my shop manual, a leaking check valve can cause a loss of residual pressure in the wheel cylinders and allow air to enter. I would really like to get the correct original return spring and reassemble the master cylinder using the same parts that you did.

[1965rivgs]

Are the brake adjusted properly?? If the pedal is solid but low there may be too much clearance between the shoes and the drums allowing for increased pedal stroke. If you are in doubt adjust the brakes tighter until the wheels will barely turn. Has the pedal come up? If so, you may just need to properly adjust the brakes. Even just one wheel will cause a low pedal.

This may sound elementary but after a complete brake shoe change the shoes may not be centered in the drum. When this is the case, during initial adjustment, one of the shoes may drag on the drum before the other shoe is as close to the drum as it should be. This leaves the impression the brake are properly adjusted when they are not. Worth a try....good luck,

Tom Mooney

[48Super]

Tom,

As far as I can tell, the brakes are adjusted properly. I went through the initial procedure but I think counting "clicks" is not a real accurate way to make the adjustment because the star wheel adjuster may rotate differing amounts each time you move the adjustment tool. I adjusted everything as best I could and then drove the car back and forth many times to give the self-adjusters a chance to take up any excessive clearance. I rotated the front wheels afterwards and there was noticeably more drag on them then when I first adjusted them. How much drag is normal? I also noticed that with the engine off, the brake pedal feels high and very firm. It goes down quite a bit when the engine is running. I know some movement is normal when there is vacuum assist, but it seems to move a lot. When I drive the car, it stops straight and without excessive pedal effort but the pedal does travel too close to the floor. I'm not sure what I'm going to try next.

[JZRIV]

Tom,

As far as I can tell, the brakes are adjusted properly. I went through the initial procedure but I think counting "clicks" is not a real accurate way to make the adjustment because the star wheel adjuster may rotate differing amounts each time you move the adjustment tool. I adjusted everything as best I could and then drove the car back and forth many times to give the self-adjusters a chance to take up any excessive clearance. I rotated the front wheels afterwards and there was noticeably more drag on them then when I first adjusted them. How much drag is normal? I also noticed that with the engine off, the brake pedal feels high and very firm. It goes down quite a bit when the engine is running. I know some movement is normal when there is vacuum assist, but it seems to move a lot. When I drive the car, it stops straight and without excessive pedal effort but the pedal does travel too close to the floor. I'm not sure what I'm going to try next.

Somehow when I read your first post it did not register that you did a total brake rebuild. I was stuck on the MC. Double check your shoe installation on each wheel to make sure all is installed correctly, short shoe leading, springs, spreader bar, ebrake cable, etc all installed correctly per manual. Its easy to get something out of place even when being careful. I always take a pic of each wheel before disassembling.

Since the car stops fine, Focus on Toms suggestion. Sounds like you're building pressure in the MC, its just that the fluid has too far to travel. The fronts are easy to spin and adjust until slight drag starts but the rears are a bit harder because you already have the drag working against you from the limited slip differential but concept is same. Spin, click adjuster, spin click adjuster until it starts to tighten up. The last rear wheel will be tougher yet because you now have the drag from the dif and the first rear wheel. Trans must be in neutral and both rear wheels off the ground. You can do one wheel at a time but you'll need to overcome the friction discs in the posi diff in order to rotate wheel and that can be tough unless your discs are shot.

As far as how much drag is normal I set new shoes up a little tighter because they will wear in fairly quick and loosen. The front wheel shouldn't spin freely. Giving it a hard spin and letting go maybe it will spin one revolution or less and a couple more with worn-in shoes. You should be able to rotate the wheel with one hand using minimal exertion. Again this is where the rears are more difficult because you have to compensate for the driveline drag.

Edited April 22, 2013 by JZRIV (see edit history)

[48Super]

Jason,

Thanks for the adjustment info.The wheels behave pretty much as you describe. I did some more investigating and found a pedal travel measurement given in the shop manual. When I depress the pedal hard with the engine running, I measure about 1-3/4" from the carpet to the back of the pedal pad. This is greater than the 1-1/2" required. So I think the brakes are actually OK. It is just my perception of the pedal feel. I seem to recall now that my previous Riviera, a '64, acted much the same way. When I sit with my foot firmly on the brake, I can get the toe of my shoe under the pedal so I know it is not going all the way down to the floor. I'm going to try accumulating some miles on it to let everything get a chance to wear in a little and see how it does. Because I did so much work to it I may have been extra sensitive to looking for problems where there were none. I really appreciate the input and suggestions from everyone here.

[Guest onedesertdog]

Hi all, Since it was mentioned about the screw on top master cylinder, this master cyl/booster was in the trunk of my 65. If the pics come out, is this the Correct one for the 65 super wildcat 2x4 non GS? Just curious. It's not like what I have on it. Also, because of you fine folks I joined the R.O.A. Just waiting on my packet. Have a great one, Buddy L.